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Old 5th January 2004, 09:34 AM   #1
wenye is offline wenye  China
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Unhappy A very hard to understand input stage

Today, I'm not so busy, than I have time to review technique paper in our company's tech-lib. I found a sch of a hi-fi power amp, and I spend many time in it. But I can not fully understand it's input yet.

I attach it below, does someone understatd it? I wanna know:
1. why the designer do so complex design,
2. what benefit with it,
3. and how to analyze it.

Thank in advance...
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Old 5th January 2004, 11:25 AM   #2
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Old 5th January 2004, 01:24 PM   #3
Previously: Kuei Yang Wang
 
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Default Re: A very hard to understand input stage

Konnichiwa,

Quote:
Originally posted by wenye
I attach it below, does someone understatd it? I wanna know:
1. why the designer do so complex design,
2. what benefit with it,
You will have to ask teh designer. The circuit is pretty basic really.

Quote:
Originally posted by wenye
3. and how to analyze it.
To start simple, the main circuit is a cascoded long tailed pair (LTP), very ordinary though a good idea to improve circuit linearity. Part of the complexity is the Biasing for the Cascode Transistors (Q3 is a simple emitter follower biasing the bases's of the cascode).

The two PNP Transistors below the LTP together with Q6 are a cascoded/super pair current source (if I read the circuit right). So again, not much of an extraordinary design. Of course such a CCS is much more "constant" than simpler circuits.

I hope that helps a bit.

Sayonara
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